I suspect it would mean I would need to change out the front derailer as well. I don't think its up to the task of shifting a larger chain ring. One of the drawbacks of cutting costs a little and going entry level. I have the Sun race m50 24 speed drive train and it works great. On the road its smooth and fast enough, I can clog it with mud and it still shifts. But I think the answer to this one may be to train my legs to the maximum limits of the bike and then look at a different bike if I want more speed.

I tried shifting down a cog and spinning faster. You can indeed maintain the same speed with a different sort of effort. Been running 2km intervals at higher rpms for the last week or so to try and get the cadence up. I think its working. Today I managed to stay anerobic for the whole interval and the recovery time was minimal.