I'm an ex-8454 owner. Between the 8455 and 8454,the main diff is, if i not mistaken,is the 8455 comes with Sirius Satellite radio, GPS (which i think cannot work in malaysia). Aside from that, i tink feature wise 8454 and 8455 share the same features. I do prefer the look of the 8454 though.. the 8455 looks a little bit ugly to me..
Anyways, I was very happy with the 8454.. it had tons and tons of features... comes with both standard and pro mode. Standard mode good if u want to run simple set up no frills set up. Pro mode good if u want to run full active... got Time Aligment, X-over, 10 band PEQ.. the whole lot. Unless you really picky over the sound, you don't have to waste money on outboard processors as the DSP from the Eclipse ihas more than enuff features to create nice music.
Only gripe i found with the Eclipse is the feature not as user friendly to beginners... Sometimes you can get really lost with all the features... especially when I first bought it... But as u get used to it, you'll love the flexibility of the Eclipse. Also,... hate the fact that the faceplate is not removable. I got my windows smashed because of this. Luckily they didn't have time to kaput my stuff.
I haven't personally played with the pioneer though so I'll let another pioneer sifu to highlight what is good and bad abt the pioneer. For me, Eclipse had served me well...