Making a distinction between clerics and magic users

After toying with adding a new spellcaster class into Lamentations I ended up hacking the existing magic user a bit as well to differentiate them from how clerics cast their spells, details of which I'll explain to you below after catching you up to speed. 

This all began when a friend of mine mentioned that a warlock-like character class would be really cool to play in the kind of setting that LotFP implies which in turn led me to find this really cool post about hacking the elf class into a "diabolist", a person who acts as a host body for otherworldly beings and is thus able to cast magic-like effects.
So of course I went and put together a version of it which reads almost exactly like the one in the blogpost, except for the fact that I dropped all the dipping into fighter class that elf would normally get. The other difference I added to the hack was that when casting a spell the diabolist doesn't have enough points for they roll on the mutations table, save vs magic and on a failed save roll on a miscast table instead of straight up taking damage.

Oh, and I did make a neat little 1d20 table of random mutations that advance to up to three different stages for the diabolist which I'll probably share at some point.

With that done, I was thinking to myself that this diabolist would now be a spellcaster class which could gamble for way more powerful effects if they didn't care so much for their safety, but also wanted to come up with some way for magic users to roll on the miscast table as well.
After having let that thought sink somewhere to the depths of my brainstuffs I came upon ideas that other people had had for magic being just that bit more volatile and powerful in their systems and toying around with some ideas this is what I came up with:

When magic user goes to cast a spell, roll 3d6. Target number here will be 10 + (spell level - magic user level) - int modifier. If the Magic User fails by five or more they roll on the miscast table. If the Magic users fails but not by five or more, the spell fizzles OR they can choose to cast it and roll on the miscast table afterwards. On a successful test the spell is cast normally. Magic users can cast their memorized spells any number they wish per day.

 I might add in an extra bit about casting non-memorized (read: prepared) spells from spellbooks and such takes one extra action as they need to flip through the book to find their notes.

The purpose of this is to neatly give each caster a distinct feel to how they cast their magic: 
Clerical magic is reliable but not nearly as readily available, it was left untouched and as it is in the base rules..
Magic Users can weave spells as much as they wish but there will always be a chance of things going south.
Diabolist ended up as the middle ground where they have a pool of points to spend on reliably casting spells, after which they too can risk themselves (and potentially their party) to squeeze out more magic.

With that the chaotic magic now has less limitations but does include chances of it going out of control, while the lawful magic is very strict and limited but always acts as expected.