So... here's my system:
 
EVGA GTX 980 Ti ACX 2.0
Core i5-2500K @ 4.3GHz (boost clock)
16GB PNY XLR8 2133MHz DDR3 (2x8GB)
Asus P8Z68-M Pro Micro-ATX
CoolerMaster Hyper 212 CPU Cooler
240GB Mushkin ECO2 SSD
SONY CD\DVD\BD+-RW (sata)
Case fans: 3x 120mm, 1x 80mm
PSU - read below...
 
I recently upgraded the video from an EVGA GTX 970 FTW.  Running the same setup worked fine and I was even overclocking the 970 up to around 1400 GPU and 7600 RAM.  I put in the new 980Ti and my power supply couldn't handle 3DMark even at stock speeds.  I was using a Cooler Master CX750 (purchased brand new 4 years ago), which, after a little research I had discovered it's actually a tier 5 PSU, and I'm probably fortunate that it did as wall as it has for the last 4 years.  It still works fine for lower power draw systems, the protection circuit kicked in just the way it was supposed to after running several tests... so it's worth keeping, just not for this.
 
Currently I'm using a friend's Corsair CX750M, which is listed as a tier 3 PSU.  It does the job, but it's $90 (on sale), and with the coupon code I got from EVGA I will be able to get a much better PSU for less.  So here is what I am looking at and I want some opinions.... 
2015 PSU Tier Chart: 
 
Tier 1 - My original choice, just to have the best possible
EVGA SuperNOVA 750 G2
 - $70 after coupon and shipping
 - 10 year warranty
 - Fully modular (don't care)
 - Gold Efficiency (don't care)
 - Out of Stock
 - Higher tier rating, longer warranty, BUT, out of stock and lower wattage
or
Tier 2a
EVGA SuperNOVA 850 B2
 - $60 after coupon and shipping
 - 5 year warranty
 - Semi-Modular (don't care)
 - Bronze Efficiency (don't care)
 - IN STOCK
 - $10 less, 100w more power (if ever needed), BUT, lower tier rating, and shorter warranty.
 
And here is my question.OTHER than the warranty period... are their any significant drawbacks to getting the 850 B2 instead of waiting for the 750 G2?  Tier 2a is still listed as being great for overclocking, and I'll have the extra 100w of head room.  All other things being equal, wouldn't the 850's higher headroom of power compensate for the slightly lower quality compared to the 750 G2??  I like to overclock... but not to the extreme, that take more time and dedication than I am willing to put in, too many other things to do (kids, career, etc).  Any benefit to waiting for the 750 G2?  Or just get the 850 B2?

OP, what did you get?  I have a 50% coupon, too, and I am debating getting the 850, even though my Corsair AX750 is handling the job well.  The 750 is plenty for my single 980 Ti, but just thinking of having a backup PSU for half price.  I am looking at the 850 with the 10 yr warranty ($160 model).
 
Thanks

Vlada011
Why backup, I would go on EVGA 850 P2 for primary PSU and AX750 for backup.
This model is 20$ more but Platinum..If you want gold you can 850 G2. Both of them support Eco Mode.
 
http://www.evga.com/Products/Product.aspx?pn=220-P2-0850-X1
 
850P2 is newer and better if someone want smaller PSU.
 

Well, the 750 is already installed and running fine and I did not want to mess with it until I start my upgrade path (i.e. MB, CPU etc) and then I would crack the system open.  In the mean time, it would serve as a back up just in case something did happen to the 750.  
 
I just don't want to waste the 50% coupon.  Also, I did not see the P2 on the eligible list, which is strange because they have the 1000w P2 on the list.  I may have to call them to verify if I could get the P2