I am an extremely poor sailor and the

is a relatively poor sailing boat; however, I have not only clocked up a fair few hours sailing larger yachts, but during 2009 had the benefit of some one-2-one trim training on the Mac when I was in Dubai. It's like riding a bike; initially baffling and a little daunting, but once you have grasped it, it's largely instinctive.
In the conditions you describe sailing on the Main alone would be a hiding to nothing, as the Centre of Effort will be way back and the boat will tend to weather up as it heels (especially in gusts); the rudder angle necessary to compensate will inevitably create drag, which will slow you down and compromise tacking. Beating into 20mph of TRUE wind the full 150 genoa is certainly overkill, but if you reduce sail, move the cars forward and tighten the sheet in (to move the belly of the sail downwards and backwards, and give a finer entry point in spite of the smaller and consequenrly higher sail) you should be able to point moderately well without continually luffing up, and thereby maintain enough momentum to tack. I would recommend full board down - although this may reduce Speed Through the Water, in a light boat with a high profile like the Mac it will improve Velocity Made Good towards a windward mark quite significantly.
The Main itself needs to be reefed, flattened and untwisted in these conditions; slight luffing is not a major concern, as you have surplus power in the Genny in any case, and in this situation the Main is providing balance rather than forward motion. On the beat, let the Traveller out to leeward, make sure the halyard and the outhaul are really tight, and play the Main Sheet in the gusts rather than the wheel. Remember, the Genny is driving the boat, the Main is controlling the heel and weather/lee helm by opening or closing the leech*. The key to this is to tolerate the
windward telltale fluttering out slightly, rather than streaming back (as the leeward one should be doing if properly trimmed).
*Closing the leech of the Main increases heeling forces, thereby increasing weather helm and causing the boat to round up; counter this primarily through the position of the Traveller (and to a lesser extent the Main Sheet). If the gusts are moderate rather than severe, you may get better VMG upwind by leaving the Main Sheet and Wheel completely alone and playing the Traveller until the sail is
just starting to luff. Constantly turning the wheel will slow you down - as another contributor has commented, if you need more than 10 degrees of rudder angle, you have a trim problem. I would add that if you are consistently heeled at 25 degrees or more, you are probably flying too much canvas; reduce both sails in similar proportion although, as the size of the furler- Genny can be fine-tuned whilst slab reefs in the main are fairly crude adjustments, reduce the Main first and more.
I do not have vast experience of competitive racing or sailing the

above F4, but in my case wave motion is almost always a bigger challenge than wind strength. In these circumstances I favour "punching" power over pointing angle, and consequently tend not to flatten the sails too much. At sea, in 15 knots TRUE and heeled at around 20 degrees I can typically maintain around 4 knots SOG at 45 degrees to the APPARENT wind, although VMG towards a windward mark is
far less due to leeway and the the fact that the apparent wind moves forwards quite significantly, such that I am probably closer to
60 degrees off the TRUE wind. Hope this helps.