it might be just as cheap to change the 36T small chainring for a 34T. If you go to a 28T rear sprocket your rear derailleur might not be able to manage it (unless it is 5700 series 105).

this depends on your rear deraiiluer, you need to research if it will support a 28 tooth cog on the cassette

An 11-28 or even 11-32 would aid you greatly just make sure that your rear derailleur can handle it. If you have a mid to long cage, 11-28 would be fine regardless.

I have done just that and it works fine. I can't tell the difference. I think the difference is just to do with tooth profiles for easier shifting.

No problem.
I feel lighter than 5600.

Hi - I am running the same deraileur / cluster with a compact (50/34) chainring and it goes fine.

it will run fine, its what I use.

Yes

The cassette comessupplied on a plastic hub which has a 1mm spacer attached which you will need at time of fitting.

Yes, it actually will! When researching before my purchase I found that the advice on the Internet was contradictory and often incorrect.

In the end I took a risk and am happy to say that it does work just fine on my short cage (SS) Shimano 105 derailleur. It works in all gear combinations including the "non recommended" ones like the large chainwheel and the largest sprocket (i.e. 50T at the front with 28T at the rear).

Btw I have a compact chainweel set (50-34) at the front.

No. I've tried it, went back to 25t.

yes - I've used 105 5600 and 5700 cassettes on the same wheel without any problems.

pretty sure you can, its only the newer cassettes with the 11-28 teeth that need to upgrade to latest rear deraillers

First, toss the chain - it is past its used by date - which can be confirmed with a chain stretch tool (fancy looking ruler) or by a mechanic at your LBS. I believe the 105 5600 rear derailleur was designed for a maximum rear sprocket of 27T hence the lack of smoothness with a 28. A Shimano 5700 rear derailleur or a SRAM derailleur should cope with a 28T sprocket

new derailleur or new lower chainring may be worn out, they do wear out. Possibly, try another high quality (Wipperman brand) compatible chain.

It would run just fine.

f they have a non-indexed (i.e. friction only) option then yes. Obviously an indexing mech will have problems with the degree to shift the cable for each gear-change.

Yes it is supplied