The 2005 Bonneville SLE got the Series II 3800.
They are very similar to the GXP, except they got the standard one piece spoiler (GXP got three piece) standard SLE brakes (GXP got bigger brakes and dual pison calipers up front) standard oval exhaust tips (GXP got dual outlet staggered chrome tips) and the regular SLE / SSEi interior (GXP got faux carbon fiber trim pieces and aluminum look shifter handle and door handles) 17" chrome five spoke wheels (GXP got 18" painted five spokes"
That said, anymore with the gas prices, the 2005 SLE really isn't that much cheaper if any cheaper then an 04 / 05 GXP and not to mention are actually quite a bit harder to find.
1982 Cutlass Supreme - mild SBC, tons of fun! The summer toy
1996 Silverado Z71 - the hauler
2002 Bonneville SLE - His / project
2003 Bonneville SSEi - Hers / never ending project black mirror