How fast should I be doing my swim sets

I would defer to TJ on this (and pretty much all things swimming-related), but I'd ask if you could do either the 'bad' or 'good' for the same workout.  That is, if the workout was 10 x 100 with roughly 15" rest, could you hit all the intervals at 1:30 with 'bad' form?  Or do you die after 2 or 3 and fade towards 1:40 or slower.  If the former, your 'bad' form may not be as bad as you think.  If the latter, then you probably already have your answer.

Again, if TJ says he's seen this a million times and do the 1:50s, regardless, then listen to him. 

FWIW, I can hit a similar pace as you on a very hard 100.  But then I am gassed.  To do the set I listed above, I would need to swim at close to 1:40s.

Thanks for the info guys, I am following the swim plan in the BT HIM 20 week plan. For instance yesterday was

WU 250 bilateral

400 / 4x100 / 300 / 3x100 / 200 / 2x100 long were RPE 4, 100's RPE 7-8

CD 3x75 each one slower

I'm doing a pretty much the plan to the T, the only real difference is when it guves me a pull or kick set, i just swim those with good form. So my plan has a variety of long sets, 100's etc etc. I see next week I have a 20x75 coming up.

Probably the biggest difference in my swimming from last year is volume, I'm just got started for the year Feb 1 and have been swimming 3x per week at 5-6k total whereas last year I averaged about 5k per month, with a high month of 8k. I'll be at about 25k this month, so there ya have it.

Not the 15-20k per week like some of you, but a big increase for me, I'm sure once IM training starts in July my numbers will go up more.

Sorry about the first post, for some reason when I post from my iPad even though I space it, it bunches it all together.

I think you're right that the bad form probably isn't that bad, but if you've made changes in your stroke then you need to give yourself a grace period on performance, and you will see the times start dropping as the new form becomes normal, hence the slower interval to start with. So in the set you mentioned, you should have a 7:20 interval for the 400 (not goal time, but the time you push off the wall for the next repeat) and 100's on the 1:50. That's probably going to get pretty easy pretty quick, so if you find yourself sitting on the wall for 20 secs in the 100's, then you need to bring that interval down. Also, do some pull and some kick sets when they're prescribed. There's a reason for these sets.

I am in a similar position as the original poster.  I was only swimming 3500 yds a week and stuck at a 100 interval pace of around 1:45 to 1:50.  After doubling my weekly volume for the last month, I am now able to do 10x100 on 1:55 with all 100s at 1:35 or faster pace.  Often I can do the last 3 sub 1:30.  The problem is that my form still looks terrible.  I had someone videotape me the other day and I look no better than I did in October, same crossover problem, not enough rotation, parachuting kick with one leg, you name it.  But I am significantly faster than I was in October.

Should I still incorporate a lot of drills into my set to try and fix my form?  If I do drills it always lowers my total volume for the workout since I don't have 90 minutes to spend in the pool during the weekday.  If I can swim the final 3 100s in a long set at 1:25 pace, does that mean my form may be good enough and I should just keep swimming harder and longer sets?  I have a feeling that if I fixed a few flaws in my stroke (and there are many), I could drop those interval times below 1:20 pace at an easier effort.