The 6.5X55 is a very good performer, and the rifle you have in mind is an excellent long-range shooter with the cartridge. A UKBRA member has regularly taken the 'Factory Sporter' class in 1,000 yard BR comps here in the UK in recent years with this combination.
The cartridge is an easy enough one to load for. As others have said, most US data is geared to that for 100 year old M1896 Swedish Mauser service rifles and a limit of around 45,000 psi peak chamber pressure (or in some case considerably less even) is used. The European equivalent to SAAMI, the CIP has recognised a modern version of the cartridge, the 6.5X55mm SKAN for use in modern rifles such as the Tikka you have in mind - its MAP is 55,000 psi, substantially higher. If you can get Vihtavouri propellants where you are, Viht's online rifle reloading data has two versions -Swedish Mauser and SKAN with heavier loads for the latter. Even if you don't use Viht, you can compare the two to see what is a safe % increase in the maximum charge and use it a guide with those you can get - eg the % difference in maximum charges for Viht N160 will be reflected in loads for IMR and H4831. For example the maximum charge for the 136gn Lapua Scenar match bullet rises from 45.2gn to 47.1gn, an increase of 4%. That level will be reflected across the board and can be adopted for equivalents such as H4831 - as always increasing charges in small steps (0.3 to 0.4gn) and looking for pressure signs
http://www.vihtavuori.com/en/rifle-reloading-data
As earlier posts say, the cartridge likes slow burning powders. My favourite is the very slow burning Viht N165 for 140s. Teamed up with the 140gn Berger LR BT it makes an excellent long-range loading and at Vihtavuori's SKAN Maximum is still producing under 55,000 psi. Use Lapua brass - expensive but better than US cases and it'll last a long time at standard 6.5X55 loads. If you're still worried, well just stick to the reloading manuals' maxima - even at 45,000 psi you will get excellent performance, such is the very good external ballistics performance of 6.5mm 130-140gn bullets. Your barrel and brass will last a long time too with these loading levels.
Minimum listed loads for your 7mm RM will be perfectly safe to use as recommended as your starting charges, but you may see a warning not to use still lighter charges with some powders. In a large case an overly low charge of slow burning powder can in very rare circumstances detonate instead of burning progressively producing the same effect as a massive over-charge.
Different cartridges use different loads even if using the same powder and in the same bore calibre loading the same bulelt - eg 7mm-08 v 280 Rem v the 7mm magnums. Pressure is heavily and directly influenced by combustion chamber volume which on initial ignition is that of the cartridge case. The larger the case volume, the lower the pressure, and the greater the powder charge needed to compensate. Water capacity is the standard way of referencing case volume. (Weigh a fireformed unsized case fired in the rifle empty, then again filled with water level with the case-mouth - the difference is the overflow water capacity measured in grains weight for that make of case when fired in your chamber.) The 7mm-08 has capacities in the 54.5-56.5gn bracket; the 280 Rem runs ~ 68gn, and the 7mm RM ~82gn. With a 50% increase in case capacity over the 7mm-08, the magnum both needs and uses considerably larger charges - basic internal ballistics rules. When there are large differences as in this case, different burning speed powders are usually called for too, the larger example often needing slower burning powders. This is why most people load the 6.5X47mm with VarGet and Re15, but the considerably larger case 6.5X55 will use the 4831s and can even accept H1000.
As a complete beginner to handloading, you may find it worthwhile to buy a copy of Glen Zediker's new book 'Top Grade Ammo' (A step by step guide to creating quality ammo) Although geared very much to 308 and 223 for Service Rifle competition in semi-auto rifles, these issues, components choice metrics etc are explored telling you why you do things certain ways as well as recommending how you do them.
