I concluded I was "FF ready". Of my lenses less than 10 are APS-C only, more than 25 are FF compatible, and a handfull are usable on FF even though they are DA lenses.
When I stumbled upon a lightly used K-1 there were two things I didn't have for FF ; a wide angle and a standard zoom.
* The K-1 came with a DFA 28-105
* I found a very nice A 20/2.8 on a local marketplace shortly after I got the K-1
The APS-C lenses that are painful to leave behind (yes, yes, I
could use them in crop mode or on my K-3, but in practice I don't):
* DA 15
* DA 21
The two DA lenses I find very useful on FF even though with restrictions:
* DA 10-17 (works just fine at 14-17mm)
* DA 55-300 (vignettes quite heavily at shorter focal lengths, but at 300mm I find the images usable without cropping and excellent with a slight crop)
The one DA lens I find fully usable (and use a lot) on FF:
* DA 70
The one lens that went from "meh" to wonderful when going FF:
* FA 31
Do I care about lower FPS? Not really. I have shot a very few high-speed series with the K-3 on safari but they haven't really resulted in more keepers than a slower shot rate does. The other thing high FPS is useful for is hand-held bracketing, but with the DR of the K-1 I haven't felt the need for that.
The big question, of course, is: Do I "need" FF? No, I definitely don't. In fact, APS-C is probably a better fit for my needs (less weight with more reach). But I still find the K-1 more enjoyable to use, and as such makes my hobby more enjoyable. Which is why my K-3 sits on the shelf even in situations where it really would be a more suitable tool.
What am I lacking? Nothing much, but I have two items I hope Ricoh will make one day:
* A small and lightweight DFA 20/4 Limited (a FF version of the DA 15 Ltd, if you will)
* A (relatively) compact tele zoom, something like a DFA 100-400/4-5.6 at 1.5 kg. Not likely to ever happen but one can always hope