I don't think adding 8-10 new fields will slow down the odoo server. but again it depends on the logic/calculation you are using to get the value of the calculated fields. don't forget to try to make the fields storable because if the field is calculated fields and if it is not stored, odoo will calculate the value each time you try to access the record (in list view, odoo displays by default the first 80 records, so for all these 80 records odoo will calculate the values that cause a performance problem) but if the calculated fields are storable, it will not cause a major performance problem