I'd give it the big heave-ho full-on pb attempt. Put all that marathon training fitness to good use. After all, you're just as likely to pick up an injury in another session anyway. Worse case is you run VLM next year.
HL: Looks like you're heading in the right direction but I'd say you need to be nearer to 60/70 miles at least by then. Some have got under with a 1:29 HM but you probably need to be closer to 1:25. You're pretty young but April's not that far off; If I had to make a bet I'd say you'll have a better chance the following year....good luck though and stick around. Plenty of sound advice around here.