@jamma your stats compared with mine
Your avg speed is 14.74mph with 37.82ft/mile, this year I have done 13.53mph with 49.8ft/mile mostly commuting, with a bike weight of 14+Kg, from your latests stats you have increased your speed, I can do 15+mph over 20-30 miles again bike being 14+Kg (with mudguards) with a similar elevation to yourself, but you need to keep at it, ride as often as you can and listen to those on here who know better about TT or racing.
The best local 10TT I did was 26.33 18.3mph, (same bike though not at 14+Kg) that was a few years back but only a year after I starting cycling a little more seriously.
As for a turbo when weather is bad, races are held in the rain so its a good idea to ride in it to get use to it.