Certainly some interesting an complex questions that can be investigated only with reference to scale drawings at the same scale.
1. Russian Guns weight of carriage and gun tube were lighter than the Gribeauval Guns
2. Gun carriages were larger as they used Baltic Pine rather than oak in construction. The latter is denser. Many Royal Naval ships were made of ths due to the lack of oak in the late Napoleonic Wars.
3. Unicorns were gun howitzers and fired over a shallow almost gun trajectory.
4. Russian limbers had ready to use ammunition those of the French using the M1765 8-pdr limber did not except for the very small coffret that had to lifted on and off the carriage upon limbering.
5. Despite drawing all these to scale I have not measure the width of the iron tyres for both. Something that might be of use.
6. The Russian M1805 limber could be pulled two or three abreast rather than by two for the French. The first line of horses have more traction power than the next etc...
7. The draft horses were different between nations. This influenced the angle of draft due to the length of the legs of the horse.
All these I have collected various papers. As an excellent start is the paper by Paul Dawson on this site looking at the French drafting and horses.
The lightness of the M1805 system was excellent for the improvements of the time with better gunpowder. This meant that you could use a lower charge weight and hence shorter barrel than those that had been developed 50 years before. In 1732, the optimum length was about 20 calibres, reduced to 18 calibres in 1765 and by 1800 to 15 calibres. There were reducing gains over length. The shorter the tube the lighter and quicker it is to load. Lower powder charges means you can carry more ammunition etc...
The Russian Caisson was more mobile over rough teraine than the M1765 Caisson which was by this time outmoded. Its high centre of gravity and small front wheels were a real problem. The best designs was the British Desaguliers Ammumition Limber Caisson. The use of ammunition boxes was far superior to the individual round supply methods of the French Gribeauval. Adopted by the AnXI System and abandomed due to financial constraints. This is the grey area.
I hope that assists a little. Your questions are difficult to answer without illustrations. These are in our book DDS (2007) Napoleonic Artillery. Alas I drew them to scale but the publisher ignored this. Eventually NGA Archive will be producing plans of the various Ordnance Systems. The Dupin drawings made in 1816 of the British Ordnance are in Summerfield (2009) Dupin's British Napoleonic Ordance, DP&G.
I am just going through the proofs of the Saxon Artillery 1733-1827 and the illustrations I think set a new standard in the drawing of Napoleonic Ordnance. The best drawings are by the wonderful draughtsman Norman Swales and mine after many hours of tutoring by hims are getting there. The use of colour certainly assists the reader in understanding the 3D nature of the pieces.
NGA Archive will be producing some of the drawings as four A4 Colour plates at 1:24 scale per set with a uniform plate and are accompanied with 4-6 page explanation. This is a start of a new series that will be developed. For those who wish to discuss this then please contact me or Gerard Cronin, the well-known uniformolgist and figure painter.