generally the answer is contained here:
and no we don't release anything with 'lots of bugs'... @jaffasplaffa comments is I think a little misleading, as with all software, any particular bugs severity will partially be down to how it impacts your work and workflow. i.e. its a minor irritation to some, and major to others.
... I use the development version at all times, so would hardly let a major bug stand.
yes, you can have two different versions install on different computers, and in fact even on the same computer in different directories, in the current release, the later requires you to manually set an environment variable, in 1.0.10 this is made alot simple as its supports 'versioned' instances.
but as with most software, you cannot use patches/objects produced with a future version. e.g. 1.0.8 can use anything prior to 1.0.8, but not post (e.g. 1.0.9 )... from 1.0.10 we actually enforce this.
hence the recommendation, if you are doing something for a performance use the released version, as if you hit a bug, you don't know when it will be fixed. BUT if you can afford to wait, then it will be fixed in a subsequent test build... (thats the point of test releases, to uncover issues so we can fix them!)
so... my recommendation
have 1.0.6 installed, on one machine for performance use.
install 1.0.9 on another, with a copy of stuff from 1.0.6....
do major changes to performance stuff on 1.0.6, but otherwise do future development work on 1.09, and also use it as a chance to test and see how your going to work with 1.0.9+
(once 1.0.10 is release, this will become easier)
oh.. and both @johannes and I do recognise, this test cycle was a too long, and we really need to have the stable version released, this is the priority.
with the post 1.0.6, we decided to try this 'test' cycle as a release process, to encourage feedback and early access and testing ... but Id say its only been partially successful. so I think we will probably need to review the approach for subsequent releases, and either modify it, or do something different... but we will have a bit of time to discuss this whilst in the next development cycle.
( my main goal would be shorter cycles , but frankly, evidence is that this will be tricky in the short term)