Most that have switched from Toner to inkjet have had minimal complaints from customers about quality and the color matching can be done better with the newer HP heads using pigmented ink. Not heard anyone talk about issues with reprints hitting same colors again. Speed is a no brainer, inkjet kills toner in that respect.
Toner is good if you want to match letterhead exactly to envelope or have really picky high end clients that do low volume runs.
Inkjet will require more volume, not a ton more but I would say 20k minimum per month if you have a lower end memjet and keep it cleaned and maintained.