Perhaps you may gain an advantage by pacing the first half at sweet spot but not at the lowest end - rather a little higher - then at the midway point where you have said there is a potential for a bit of recovery, do a bit of a self ‘check’ and see how you feel.
If you feel good and strong then you can select a power that you know might otherwise be challenging (for example threshold) and really dig deep - on the other hand if for whatever reason you are not feeling so good, stay in sweet spot but at the higher end.
Then (and this is the fun bit) when you get to a point in the road that means you know (from your previous test ride of the route) that you have about 4 or 5 minutes to go, take another ‘check’.
Again, if you are not feeling great just continue with the higher end sweet spot and try to hold it to the end - pushing for a sprint out of the saddle if necessary, when the finish is in sight.
However if you are feeling good then consider a bigger effort for the last 4 minutes - just above threshold or Lower end VO2 max. Again with a dig deep push when the finish line is in sight
This approach means you have two ‘review’ points in the race at which you have already decided upon your strategy in the event of feeling good / not so good and this means you don’t have to think through a decision on the go and can implement the already decided plan which will give you confidence and save you any mental effort on the day.
As a bigger guy you probably need to factor in that the ramps you’ve mentioned in the second half of the route will have a greater impact so the steady pacing in the first half will allow you preserve yourself a bit for the effort ahead.
If on the other hand you smash the first half then you may end up losing any time that gains you, through reduced energy over the second part.
I’m no expert and don’t have a huge amount of personal experience of this type of effort / race but have been told by a quite a few different more experienced racers that it is almost always better to finish strong that go off hard and fade later on. I’m a bigger rider too and have found that psychologically this approach is more helpful as it leaves a bit in the tank for the point at which you know the end is in sight and then you can use the extra mass to your advantage (if possible) to basically try and empty everything in the last couple of minutes.
With this length of effort don’t forget to consider you pre and mid race fuelling - my own personal recommendation (but you’ll need to play to your own personal preferences) is to try and drink your carbs so you make sure your topped up properly from the get-go - not much point taking a gel with 10 minutes to go as it may not get into your system and could make you sick if you’re smashing a PB power effort so if you think you may fade in the last half then try and top up before that.
Hope this helps - good luck