What is the best gear combo for me on road bike?

Great to hear you seeking to go faster!

What you can consider first, is your cadence.
Cadence is critical as is determines what kind of pedalling you do, basically aerobic or anaerobic efforts.

If you are aerobically-inclined, you tend to spin at a higher cadence (probably 90RPM).
If you are anaerobically-inclined, you tend to spin at a lower cadence (probably 70RPM).
*anecdotal statistics

On a ride, your cadence definitely fluctuates, but there will be a range that you find most comfortable with. From that cadence range, it will be easier to extrapolate the gearing that appeals to you!

To find the exact gearing, there are online calculators that I found useful to me!
Bikecalc: Basic but great variety of calculators to easily find the statistics.
https://www.bikecalc.com/speed_at_cadence
Bicyclegearcalculator: Great for considering climbs. +estimated power.
https://www.bicyclegearcalculator.uk/derailleurgears.htm
The computational cyclist: Does not consider gearings, purely estimated power to speed.
https://www.gribble.org/cycling/power_v_speed.html

Personally, Bikecalc has been very useful. It highlights different groups of gearing ratios whether it's harder or slower as a reference point.

Be that as it may, trying to get faster by experimenting with different gearings might not be the most sophisticated method.
As you did not list your exact cassette sizes, I'm using 50/11 as an example.
From Bikecalc, 50/11 at 60RPM is already more than 20mph. (IRL factors omitted)
In track cycling terms, 50/11 gives 120inch. Which is very hard.

Good to see you trying, good luck!

It's a question about physiology first and hardware second. The people that really are better off with a high gear higher than you have now are some combination of pros and/or low-cadence pedal mashers. Figuring out what cadence is really right for you given adequate conditioning is one of the key questions in cycling, and one that you can read endlessly about.

A closer cassette will give you the benefit of closer intervals between gears. If you don't need the 34 with the terrain you ride, that is all upside. The 50/34 compact, 11-34 cassette setups are good for a certain kind of cyclist and terrain, i.e. casual or beginner road cyclists with major hills or mountains to deal with, but can be serious overkill for other use cases, like rolling terrain and/or a stronger cyclist.

If the Apex group you have is still in good shape and you're finding you don't need gearing as low as you have, there's a lot to recommend just getting an 11-28 or 11-25 cassette rather than completely reinventing the bike, plus a new chain. I'm fairly certain that the WiFli type Apex RDs can handle whatever large cog you want to go down to and not have overly large gap.

A good way to begin to learn how to answer this question for yourself is when you're on your rides, keep track of what gear combination you use to climb the hills you work with, and, on the opposite end, if you find your high gear isn't high enough, what gear combination is that (50/11 for you). Then go home and plug those numbers into a gearing calculator and you will know what your ideal range is. If you need or really want to switch groups, you can let that be your metrics.

In contrast to Nathan, I would argue for a 50/34 crankset, usually called a compact crankset. This helps ensure that you have an easy enough gear. I would argue that objectively, amateur riders should stay away from 53/39s (sometimes called standard gearing, basically used only by professional riders these days). I am a fairly strong rider, and I find that on my 52/36 (aka semi-compact crankset), I never use the 11t cog in the Midwestern US, and I would probably only rarely use it mountainous terrain (on the descent, obviously).

I would argue to choose a large cog based on the terrain you expect to encounter. If you feel like a 34t big cog with your 34t front chainring is too easy a gear for your usual terrain, you can get a smaller cassette. How much smaller is unfortunately something you'll have to figure out with experience and perhaps a gearing chart. You can look up the cog sequence on your cassette. If you only ever shift to the second biggest cog, that's most likely a 30t cog.

One thing to note about the above: I prefer a closely spaced cassette to maintain a cadence as close to my optimum as I can. However, many people are less fussy about this; my experience is that traditional roadies probably are fussier. If you are not so fussy, you could elect to stick with a wider-range cassette just in case you move to or take a vacation somewhere with steeper climbs.

It depends on you, the terrain, and what you want to do.

For me , Being an A- or B rider depending on the club, living in a very hilly to mountainous area, I put together my own gear ratios that I ordered from a magazine (back then no internet!).

I chose a range of 24-105. I was limited in the available gears and what would fit and still work. This was back in the 15 speed days. Now I would probably try for 18-101 if I were still able to ride.

105 was a tad high but on level to slightly downwards I could push it okay. 24 was just enough for the worst hills but I would have liked it to be a tad lower.

17 was my best speed in a time trial. my average depending on terrain would be closer to 12-14. But I rode for distance not for speed.