Had similar dilema 6 months ago changing 3880 to a new machine.
Also duel between P800 and Pro-1000, also more B&W than color (B&W in artistic part, color for friends, some artistic and casual).
Have seen test printouts of the same photos by both printers on papers well known for me. Some facts (objective) and conslusions (subjective) and practical info:
1. I like matt B&W printouts from P800 (Epson is excellent, Canon is very good). As for gloss, both are comparable for me.
2. I love how P800 works with Epson Hot Press papers in both colour and B&W - amazing, especialy if v.2 profiles form Epson US used.
3. I like colour prints from Canon, Chroma Optimizer gives them special look. On the other hand, I do not like that angles of proper viewing becomes narower due to CO use. Out of those angles, the sufrace starts to opalize in unnatural manner.
4. Colour gamut for reds and blues is visibly wider for Pro-1000. Especially reds are important for me, frequent case od various saturated, darke reds, especially for dresses of photographed models in studio.
5. I like, that Pro-1000 carts have 80 ml of ink which is used for printing. In case of Epson carts there is around of 65 ml of usable ink out of declared 80 ml. You should have the same in 3800 case.
6. As Mark has written, I am dissapointed that P800 has no information of ink use, step back compared to 3880 where you could get this info form printer menu or after nozzle check test. P800 is not supported by LFP Remote Panel application. Pro-1000 shines here.
7. P800s have quite often some problems with pizza wheel marks (the same construction as 38xx) and rubber paper advance wheel leaving some marks while takin SOME papers.
8. Canon B&W inks are much more neutral than Epson ones which are warm therefore need to be neutralized on paper with a tiny amount of colour inks. Probably the same stands for Canon, but colour particles are mixed in the ink itself. For me, it doesn't matter since most of my B&W prints are warmer than cooler.
9. For Epson you have famous Quad Tone Rip software for excellent B&W prints, where you can control very datailled aspects of printing (but quite challenging). For Canon there is TrueBW, more familiar use, but not sure if Pro-1000 is supported.
10. For P800 you can convert your printer (now or in the future) for B&W inks (MIS or Piezography) for ultimate printing with QTR. No such an option for Canon.
I have chosen P800, mostly beacuse I know Epson system (my 4th Epson printer), know its dissadvantages, can live with them and mostly because I will be able to convert the printer in the future for any other B&W setup.
Hope it helps.