Yeah, the 74 defintely went though a few changes. First we had the classic 04 Acid 74 which was the last in line of many, many years of development (Suft 70->Acid 70->Acid 74).
The came the 2005 Acid 74 you're thinking about. Its a completely new design. Conacaves are gone etc. I though this board felt a bit big and by modenr standards a bit long, but it is still a favourite of mine. Very loose in a turn and with a certain kind of flow that is not easy to find. For me it planed early and easily handled 5.5 or even 5.7.
After that we got the Pure Acid 73 which was a ctually a slight redesign of previous the 05 Acid 70. This board was developed from an EVO 70 but draw out, so to say. It was a nice board any many still love it. Despite the EVO heritage, more width and less length it rode more "classic" than the 05 Acid on a wave. It handled chop very well though.
The we reach the 07 Pure Acid 74 (same shape as 08 PA74). This is again a completely new shape, based on a fast modern wave rocker and a trick v bottom. The PA74 is easily the fastest of the bunch and a very early planer and a great B&J board. But it is stillo a wav e it excels. It has a remarkable way of locking into a hard bottom turn and just track through everything. The tail feels very "solid" and needs some dedication at speed, but rewards with a very precise carve. In slower waves, there is still enough outline curve to keep the board loose. On top of this it has a nice and compact feel to it and great control in high wind. The 07-08 PA 74 is a very, very good board which is both high performance and easy to sail as well as extremely versatile. Its a favourite with the team too. A small remarks on width: The PA74 may seem very wide at 54cm, but we tested it against a 1.5cm narrower version in the proto stage and the wide one was simply a better board at everything.
Comparing 05 and 07 is not so easy. They are very different in feel but both of them are favourites of mine. The 07 does feel more "modern" in a way and for some reason the more compact shape simply feel more right. The 05 had a certain kind of flow (probably due to more rocker) which I miss sometimes, but I never got around that it felt a bit "big" and long. I think both boards have a similar sail size spectrum, the 07 maybe having a very slight edge both with bigger sails and smaller sails.
So, hard to choose. The 05 is still a very nice board and at a good price probably a bargin. The 07 combines world class down the line performance with great B&J performance in a very unusual way and is very easy to get on with. Its just up to you to choose...