Thinking of trying the 3 bladed 125grain Montecs out of my 45lb recurve for deer this year.
Whats your thoughts on penetration?

It will work just fine.

Hit them a lick with a stone or diamond hone, they'll be just fine.

As mentioned . Touch them up. Shoot a hqeavy well tuned arrow broadside shot

Good advice by the other guys. They will work fine.
Ted Nugent and his wife, Shemayne, pull 45-50 lbs and I've seen them kill African game on tv with compound bows.
I would make sure you are shooting at calm deer and broadside shots if possible.

I would use one of the many fine 2 blade heads with good steel. If you stay with Montec use the carbon version- much better steel.

+1

I'd also use a quality two blade over a three blade with a light weight bow.

+2

Although the G5 would work ok I would also choose a good 2 blade over a 3 in light weight bows. The single bevel twos cut an L shape wound and out penetrate any 3 or 4 blade out there.
You match them to your feathers right wing right bevel etc.
I use these:

http://www.eclipsebroadheads.com/new_page_4.htm

I shot the G5 Montec for several years and killed several deer out of my compound. I switched due to the fact I didnt feel like they were are sharp as they should be.

I am making the change to my recurve this year and I opted for the muzzy cut on contact 4-blade like little Freddy uses. Good luck which ever broadhead you choose.