Don't believe the manufacturers claims... The hornady 75 is actually the lowest of the 75/77 bmag length bullets tested by Bryan Litz.
The Lapua is my bullet of choice, with the Nosler a close second. I usually shoot a Berger 75 VLD at 600 yards, but the Lapua will shoot 195 to high 190's with dumped charges, the 75's just give a point or two average better, but usually double the X count. I don't feel undergunned at all using any of these at 600.
Here are the G7 Litz BC's for some of the more popular bullets:
Lapua Scenar 77gr - .206
Nosler Custom Comp 77gr - .193
Sierra MK 77gr - .190
Berger VLD 70gr - .190
Hornady HPBT 75gr - .183
The Litz tested G1 BC on the Lapua 77 is .412, and .393 ( I think...) on the Nosler and .390 on the Sierra and Berger 77's, for reference.
If your feeling all turbo, the 70 VLD's will shoot mag length quite well, and can be loaded to 3000 fps easily and have quite an advantage at that speed. Use 69 Sierra data as a start point, they have less bearing surface so it takes a bit to get the speed up there.
the 77's like to be going 2700-2750 (20 in AR) or 2850-2900 ( 24 in Bolt action) and in shorter guns they seem to like to be 2500-2600fps...The 75's seem to like 2750-2800 in a 20 in AR. Never shot them in a shorter rifle for accuracy, Which is easy to do without much fuss. You can use 77 data for 75's but 75 data is usually higher than 77's, so it doesent work backwards. The 75's have less bearing surface. With the increase in speed, you can pretty much equal out the BC 's between the two. My practice load is 75's and 23.2 IMR8208. 2750 fps. A popular load for them is 24.5 RE15, gets just under 2850 fps. ( 20 in 1-7.7 Krieger) The 8208 just meters alot better and is cleaner, and was more available at the time. I had 4000 75 hornady's ( a deal I couldnt pass up. $60/1k) ) and this was an easy answer for practice. When the last 1k or so I have gets turned into brass and smoke again, the Nosler 77CC will be the bullet i will use for practice. Used 2k of them before and still have 500 loaded left and they shot real well. Used them all the way back for a full course and ended up in the 780's. Not bad. Its a good bullet.
My favorite load for the 77's is 23.5 H4895 followed by 23.2 IMR8208, both of which will put you just above 2700 with a 20 in rifle. The H4895 is just a little more accurate and consistant.
24.0 RE15 and 24.5 Varget will do the same, just closer to 2750
A bolt action will handle about 0.5-1.0 grain more without issue. Sierra lists 2 different charts for a reason, and Hogdon data is based on Bolt guns. You might not reach max loads in an AR, but sometimes you can, chamber and throat have alot to do with it. Surprisingly significant difference for me between 5.56 NATO, .223 Wylde, and .223 CLE Match. The Nato chamber barrel I have ( FN CHF SS 1-7)can take the loads my bolt gun does and will post the same speeds as the CLE chambered AR does with less of a charge, same length barrels, the CLE loads in it are usually 100 fps less or so..... yeah chambers do make a difference! The Bolt gun has the CLE chamber as well, but will take a full grain more without issues. AND, its rediculously fun.