Start with fitment for the K7/K8. Fitment is shown in "best" performance first. Tyres outside this range will perform more poorly as the bead "pinch" starts to be pronounced.
FRONT (2.15 x 19 rim)
--Size-- Height
3.50-19 25.8" (recommended, speed rating S or better preferably)
90/90-19 25.4"
90/80-19 24.7"
100/90-19 26.1"110/90-19 26.1"
100/80-19 25.3"
Note: Selecting a tyre of different height than the recommended will alter your speedometer reading
REAR (2.5 x 17 rim)
--Size-- Height
4.50-17 25.6" (Recommended, speed rating S or better is preferred)
120/90-17 25.5"
110/80-17 23.9"
130/90-17 26.2"120/80-17 24.6"
I've highlighted a closely fitting wider alternative to the recommended sizes. You can select other combinations for your particular performance needs.
Note, for example, as the height of the front tyre increase, relative to the rear tyre height, cornering is adversely effected in favour of more straight-line front-end stability. Conversely as the rear height increase, the bike will turn into corners better, but will be less stable in straight-line tracking. Since the recommended combination is fractionally lower rear, it suggests the designers had improved straight-line tracking in mind. Shock height and other settings can/do offset tracking and cornering in a similar manner.
Some of the fine brands that make the ones I've highlighted (and more) and available on the net are:
* Metzler Lazertec M/CTL (100/90-19 57H Front) (130/90-17 68H Rear)
* Avon Roadrider (~90/90-19 Front) 52V (120/90-17 68V Universal/Rear)
* Bridgestone BT45 (100/90-19 M/C 57V/H Front) (130/90-17 M/C 68V Rear)
* Dunlop Elite II (MM90-19 61H Front) (MT90B17 76H Rear)
* Continental TKV 11/12 (100/90-19 M/C 57H Front) (130/90-17 M/C 68V Rear)
* Michelin Macadam 50E/50 (Hard to get) (100/90-19 57V 50E Front) (130/90-17 68V 50 Rear)
~ closer to recommended
Edit: As per your original post/question - Avon Roadriders are closer to recommended, but the Dunlop 404s would be a better looking fit. Also, I believe the 491 Elite's are newer design and compound. (I didn't know you could still get D404s).