Safe lenghts for shorter coilover springs?

[Matej]

To get to the point, I've done all the common things to my coilovers to make them go as low as possible, yet I'd still like to go lower, so I've been looking at shorter springs.

The stock springs are 180.8 front, and 200.6 rear. First number being the length in mm, and the second the rate in kg.

Here is a list of available springs I could possibly use.
Front:
150.8
135.10 (too crazy?)

Rear:
180.6
180.8 (swap the fronts to the rear and save money, but the car would sit slightly higher than with the 180.6, which would bug me forever)
150.8 (too crazy?)

I'm sure I'll most likely end up going with the 150.8 front and 180.6 rear. The only thing that somewhat bothers me about this setup is that I already have a very noticeable "raked" look going on, and this will only increase it.

However, it's really tempting to do something like 135.10 front and 150.8 rear or 150.8 all around, although I'm sure those sizes are way too crazy, and I need some to talk me out of it, haha.

That's why I made this thread. What do you consider an acceptable length for shorter springs?
Is 5cm difference too much, especially since my rears are already drooped? I'm guessing the shock would most likely bottom out and blow very soon, as I'd be ramming metal into metal.

By the way, yes I acknowledge that no shorter spring is good for the coilover.

One last question.
Which companies make separately sold springs for coilovers? These are just Megans I'm looking at since my coilovers are Megan. I know there are other brands, which are also most likely more reputable, I just can't think of any right now. I'd like to see what lengths and rates are offered by other brands, maybe I'll find something more suitable.

Thanks for any info!