Gearing

I speak with only a really basic knowledge so please correct me if I'm wrong. My experience is only of a couple of years of road cycling (club level) and 5 years of riding fixed. I've only done of couple of TTs.

Hmmm. I personally believe that if you very gradually build up to it over time you'll probably be ok. This is my very humble opinion. There are too many experienced riders out there turning big gears on a daily basis who don't have any problems for me to think that you are certain to cause yourself damage. I think its a bit much to suggest that Tom is going to knacker his knees because your Dad did.

So long as you get cause and effect sorted here:
Experience riders are riding on big gears because they are strong/fast riders.
Experience riders are not strong/fast riders because they have been riding big gears.

AFAIK the conventional wisdom is that your better off training for cadence and endurance first, then increase speed and power and reduce the length of the rides.
It's in the later stages of the training that your going to be riding shorter, faster and on bigger gears.
You may (perhaps) actually be better off going back to a lower GI and working on your cadence before working on speed. You still have time to do this before the season starts.