Speaking as someone with an Alpha Station conveniently as a footrest...
I'm calling a double bullshit.
First of all the parent: 1.2GHz for 800 when Pentiums were 433MHz?
21164 Alphas, topped out at mostly 600MHz, and were faster than x86 clock for clock. They were also pushing the MHz limit at the time, being the first to 500MHz, and using a slightly later 533MHz (21164PC) they were damned fast compared to any x86 chip. As far as speed, at the time, they were overall the undisputed fastest processors. (DEC only made up to 8 processor machines as I recall. At least I think that's the limit for the 8400, a quick googling shows a reference to 12 processors, so it's likely higher)
21264 Alphas, were mostly released at under 800MHz, while air-cooled chips were demonstrated up to 1GHz, they weren't available. They were a lot faster per clock. (Of note, the Athlon used the EV6 (21264) bus which was one of the big reasons it did well. Plus a lot of DEC engineers going to AMD following the DEC/Compaq merger, which was if I recall correctly just before the 21264 was released, I don't recall any actual DEC hardware) Near the end P4s were released so you may be thinking 466MHz Alphas vs 1.2GHz P4s. (Where the Alphas would lose on integer, they would beat the P4s on floating point instructions) Benchmarking them, they were about 1.5x as fast clock for clock as at the time the fastest x86 processor (The original Athlon, mind you this is comparing optimized builds and the alpha didn't have SIMD instructions) If you were thinking of the API builds, you might be right, if you switch the MHz numbers around.
21364 Alphas were released following the HP merger and were the only ones which were over 1GHz. At this time, it was way late. The FPU was still respectable, but overall it was a case of too little too late. The 364 was not even a new core, it was a 264 wrapped in a much better communication to the outside world, on-board memory controller, and a very hypertransport like connection. (Which predated Hypertransport, at least in the beginning of the design, but was delayed so much, that as I recall Hammer wasn't that far off)
21464 was canceled, though it had a number of things, including the first Alpha SIMD instructions.
The alpha, even the 21064s, which were petering out in favor of 21164s when I got introduced to Alpha, were not cheap. However, they (21164PCs anyway) were priced comparably to a high end x86 system. When x86 got better and cheaper, they simply didn't keep up. Part of that was due to a DEC-Intel suit/resolution, which as far as I'm aware Intel didn't hold up. Which eventually got DEC merged with Compaq. Then it was all the 'Itanium is the future', where Compaq ended up basically killing Alpha for. When HP got it, they were also heavily in the Itanium camp. HP also had their own prior processor (PARISC) which was being killed off for Itanium. Which as I'm sure you are aware the Itanic future didn't turn out the be the case.
Second:
Slow, was the one thing the Alpha was not. Expensive, rare, hot and some other things, but slow it was not. Considering that an Alpha led the SPEC cpu benchmarks for over 9 *continuous* years, being broken of the integer by P4 on release, and fpu by a much later P4 (See above for how the Alpha's frequency wasn't keeping up on the 264s)
At no time, when alpha was being sold by DEC or Compaq, would SGI (MIPS) and Sun (SPARC) hardware have been faster per processor than Alpha. Look on the SpecCPU pages, or if you can find them (I can't) the old Seti@home statistics. Hell, look at just about *any* benchmark from around that time.