So at 5 weeks prem she is around 6 weeks adjusted (she was a good size born!) so at this age bottle fed babies are taking around 4oz a feed so she's not too far off. Both mine were on a comfort formula at one stage and I used Dr Brown's bottles and I *think* level 3, they seemed ok on level 2 but changing up made a big difference. If you have Avent bottles their vari-flow teats are good for thicker formulas, Tommee Tippee closer to nature variflow are good too but are slower than Avent.
I would say the feeds are taking too long though which may not be helping. A bottle feed should be done in about 20 mins, so your LO is snacking really if feeds are taking that long and she won't be having a chance to get properly hungry by the next feed time. I would start fresh with the first feed of the day, see how much you can get in her in 20 mins and then stop the feed and see if you can hold on for 2.5 - 3 hours. If she is showing clear hungry signs then obviously feed her but she should be able to last at least 2 hours on a formula feed at this age. The other reason for not stretching feeds out is you need to discard a bottle feed an hour after a baby has started drinking from it because of bacteria growth in the warm milk.
Have a look at this link for some examples of routines
http://babywhispererforums.com/index.php?topic=164027.0 Your nightfeeds look good though!
HTH - come back with any more questions!
Laura