First of all great job so far! Going from 245 watts (previously 285 watts) to a 315 watt FTP! That is actually a pretty huge gain. Putting out your max 30 - 90 minute power as well is great!
In reality you might not make much more gains on your FTP but there is a lot more to bike racing than what your FTP is. Like a criterium will most likely come down to the last few laps, so maybe 1 minute and 20 second full gas power after 60 minutes of racing. Also your ability to position which may require several short burst in the last 5 minutes to move up and keep your position. Also road racing can come down to your best 5 or 20 minute power after 2500 kJ’s of racing. So you can not just look at your mean maximal power.
So you have this really big aerobic engine and huge base which is great! But what you are looking to do is working on your turbo and being fast! That does take intervals. Interval training is intense and very demanding. So you have to balance how much you do. Also your base and overall fitness can drop a bit during this period. Sounds like you are 10 weeks away from possibly racing and will do the 6 week criterium plan. So really just need 4 weeks to fill.
Without personalizing a plan for you the closest thing I can think that would work great is our road racing interval plan. Do the first 4 weeks of this plan. This would be some threshold work and Vo2 max. So starting to get that intensity in. But there is still some sweet spot intervals. If I were to customize this plan for you I would remove the workout on Day 7, 9 and 23. These are more full gas intervals that you will get during the criterium plan and don’t necessarily need 8 - 10 weeks out from racing. Would it kill you to do them, now, but just saving a bit of that full gas effort for when racing comes would be better. Just a personal suggestion. Could just do zone 2 days on those days.