Advice on Athlon 64 upgrade to replace Sempron 64

Esteemed colleagues:

TigerDirect (TD) has a deal that is seemingly sweet.  An AMD Athlon 64 3300+
2.40GHz, 256KB L2 Cache, 1600MHz FSB, OEM Socket 754 Processor for $20 after
a $50 rebate.  (See http://tinyurl.com/n7e54) I would have to add a
heatsink/fan for about $20.  (See http://tinyurl.com/kr3ap)  Total cost,
including shipping, under $50.

This would replace a stock Sempron 64 3100+ 1.80GHz, 256KB L2 Cache, 1600MHz
FSB, Socket 754 Processor in my eMachines T3104.  On the whole, it seems to
run pretty well speed-wise, well, considering I was previoulsy using a
233MHz Pentium…  When I bought this PC last year (another deal - $99 after
rebates), I understood going in that the Sempron 64 was not the powerhouse
CPU, and my research indicated that I could upgrade the CPU on this mobo to
Athlon 64; so I figured just wait awhile for Athlon prices to come down and
upgrade when prices hit a "sweet spot".

The TD deal is "interesting"; it specifies a CPU (AMD part number
ADA3300AEP3AR) that cannot be found on AMD's website, nor its
AMDcompare.comwebsite.  I emailed AMD's tech support last night (and
got very quick
responses -- I was very impressed!) and was told that AMD doesn't reference
OEM products on their website.  He also gave the requisite warnings of going
with OEM: only a 1-year warranty and no heatsink/fan on the OEM vs. 3-year
warranty and a "certified AMD heatsink fan" on a retail boxed CPU.  But
other than that, he "seemed" to concur that with both CPUs sporting 256KB L2
cache, the only real differentiator is that my Sempron runs at 1.8GHz vs.
the Athlon's 2.4GHz.  I asked about other architectural differences that
give Athlons an advantage over Semprons, but he never went there.

Other interesting tidbits that I can't make sense of: TD describes it as
2.40GHz, yet on AMDcompare.com, the only socket 754 CPU models that run at
that frequency are Athlon 64 3700+ and 3400+. Also, there are no Athlon 64
CPUs that have a model number of 3300+. And all Athlon 64 CPUs listed at
AMDcompare.com have an L2 cache of at least 512KB, whereas TD reports that
the ADA3300AEP3AR has only 256KB of L2 cache. There are several Semprons
listed that have a model number of 3300+.

TIA,
Dan